Even before acquired immune deficiency syndrome (AIDS) became a matter of concern, the possibility that clinical personnel might contract conditions such as hepatitis through accidental punctures by used needles was regarded seriously. Accordingly, a significant body of prior art was developed for preventing such accidental punctures.
Unfortunately, none of the prior development succeeded in producing a device in which the withdrawal of the needle from the patient's body automatically activated a protective mechanism. In each case, it was necessary for the clinical personnel to consciously perform an extra step in order to invoke the protection offered by the prior art.
One example is U.S. Pat. No. 4,631,057 of Mitchell, which discloses a guard tube 33 capable of sliding forward to protect the pointed end of a hypodermic needle 15 from accidental contact after use. This mechanism, however, like the rest of the prior art, is only effective if the clinical personnel remember to push the guard tube into its effective position after performing an injection. There is a strong possibility that they will occasionally forget to do this.
Now that the range of conditions to which clinical personnel are exposed as a result of accidental needle punctures includes the always-fatal condition AIDS, it is even more important to provide a safety mechanism which offers such personnel fail-safe protection; that is to say, a device which operates without the need for conscious forethought on their part. What is needed is a mechanism which automatically protects the pointed end of a needle from the moment when it is withdrawn from the body of an infected patient.